络合浸渍MgO改性MCM-22催化甲苯与碳酸二甲酯烷基化合成对二甲苯

以硝酸镁为前体、柠檬酸为络合剂,通过络合浸渍法制备了负载量(w)为20%的MgO改性MCM-22分子筛催化剂;在气相连续流动固定床反应器上,研究了该催化剂催化甲苯与碳酸二甲酯烷基化反应合成对二甲苯的性能;采用XRD、N2吸附-脱附、NH3-TPD和Py-FTIR等手段表征并分析了催化剂的结构和酸性,同时考察了催化剂制备过程中NaOH用量对催化剂性能的影响。表征结果显示,B酸位是该催化剂的主要活性位。在浸渍过程中加入柠檬酸能使催化剂保持较高的活性;同时加入NaOH可显著提高对二甲苯的选择性。随NaOH用量的增加,甲苯转化率稍有降低,但对二甲苯的选择性逐渐提高。

Selective Synthesis of p-Xylene from Toluene and Dimethyl Carbonate over MgO-Modified MCM-22 Prepared by Complexation Impregnation Method

MgO-modified MCM-22 molecular sieve catalysts with 20% MgO loading(20%MgO/MCM-22) were prepared by complexation impregnation method with Mg(NO3)2 as precursor and citric acid as complexing agent.Selective synthesis of p-xylene by alkylation of toluene with dimethyl carbonate(DMC) was studied over the prepared 20%MgO/MCM-22 catalysts in a continuous flow fixed-bed reactor.The synthesized catalysts were characterized by means of XRD,N2 adsorption-desorption,NH3-TPD and Py-FTIR.The results indicated that the alkylation of toluene with DMC occurred mainly on Br?nsted acid sites.The catalysts could maintain high catalytic activity through adding citric acid in the impregnation process.The selectivity to p-xylene increased significantly with adding NaOH.With the increase in NaOH dosage,the conversion of toluene decreased slightly while the selectivity to p-xylene increased gradually.